Bract necrosis

Bract necrosis is a physiological disorder primarily affecting Poinsettia (Euphorbia pulcherrima). Unlike typical plant diseases caused by fungi, bacteria, or viruses, this condition is non-infectious and arises from an internal nutrient imbalance, specifically a deficiency or limited mobility of calcium within the developing bract tissues.

The primary driver of this disorder is the plant's inability to supply enough calcium to the rapidly expanding bracts during the critical flowering stage. Because calcium is a relatively immobile nutrient within plant vascular systems, any disruption in transpiration or root uptake can quickly lead to localized tissue breakdown in the most active growing points.

Symptoms typically begin as small, water-soaked spots on the bracts. As the necrosis progresses, these spots turn brown or black, becoming dry and brittle over time. If left unmanaged, these dead tissues provide an ideal entry point for opportunistic pathogens such as Botrytis cinerea, which can significantly deteriorate the overall plant health and aesthetic value.

Environmental factors play a crucial role in the development of bract necrosis. High humidity levels combined with poor air circulation reduce the rate of transpiration, which is essential for pulling calcium up through the xylem to the bracts. Additionally, excessive nitrogen fertilization can force rapid growth, outpacing the plant's structural capacity to integrate calcium into new cell walls.

Effective management requires a proactive approach to crop nutrition and greenhouse environment. Growers should maintain proper calcium levels in the growing medium and avoid wide fluctuations in moisture. Improving air movement through fans and proper spacing helps maintain consistent transpiration rates. Monitoring fertilizer salinity is also key, as high salt levels can interfere with the uptake of essential nutrients like calcium.